Thermostatically-controlled switch



Oct. 12, 1937..

W. F. WESTENDORP THERMOSTATICALLY CONTROLLED SWITCH Filed May 23, 1934 Attorneg.

Inventor: Willem F. Westendorp,

Fig. 2'

Patented Oct. 12, 1937 UNITED STATES PATENT OFFICE THERMO STATICALLY-CONTROLLED SWITCH ration oi New York Application May 23, 1934, Serial No. 727,186

6 Claims.

My invention relates to thermostatically-controlled switches, and more particularly to an improved thermostatic latch for delaying the operation of a magnetic switch for a predetermined time after energization of the switch operating coil.

One object of my invention is to provide a simple switch timing mechanism for electric discharge lamps in which the cathodes are preheated before the discharge path is opened subsequent to each current interruption to the lamp.

Another object of my invention is to provide a thermostatic switch timing mechanism in which the time period is dependent upon the current flowing through the switch.

Anotherobject of my invention is to provide a thermostatic latch which is capable of immediately resetting after failure of current in the lamp.

For a better understanding of my invention, together with other and further objects thereof, reference is had to the following description, taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

The accompanying drawing illustrates in Fig. 1 a magnetically-operated switch provided with a thermostatic latch built in accordance with my .invention, and Fig. 2 illustrates diagrammatically the switch of Fig. 1 connected to an electric discharge lamp such as a sodium .vapor lamp for example.

Referring to the drawing in detail, the switch 3 comprises a base 4, a movable switch member 5, an operating magnet 6 and a thermostatic latch I. The movable switch member is pivotaily mounted on a pair of brackets 8, of which only one is shown in Fig. 1, projecting from the base 4. It is provided with a pivot pin 8,-a pair of contact arms 10 and i l and a latching arm i2. The contact arms l0 and II are resilient and carry contacts l3 and I4 on their respective ends. The switch arm 5 is normally biased by a spring I! and by the magnet coil 6 when the latter is energized. v

' When the switch arm 5 is biased by the spring IS, the contacts I! and H are held in engagemerit with one pair of stationary contacts I! and It. When the coil 6 is energized it tends to move the contacts I3 and I4 into engagement with stationary contacts l9 and 2B. The movement oi the contacts into the latter position is, however, subject to the operation of the thermostatic element 1. This element normally engages a pin 2i projecting from the end of the latching arm l2 when the switch element 5 is in the upper position and prevents the movement of the switch element with its contacts to the lower position. When current begins to flow through the contacts the thermostatic element is heated and moves out of engagement with the pin and permits the switch member 5 to move to its lower position. i

The thermostatic latch I in accordance with my invention comprises a rectangular piece of bimetallic sheet metal having a slightly arcuate shape at normal room temperature. Two parallel slots are cut in from one end of the sheet so as to form two relatively narrow strips 22 and 23 along the sides. The ends of these two strips are bent at right angles to the body of the strips and fastened to the base 4,'this being the means of support for the element. The ends of the narrow strips 22 and 23 are electrically connected respectively to the contacts l9 and 20 and the wide part 24 of the element, which for convenience may be called a tongue, engages the projecting pin 2| on the latching arm I2.

When current flows through the switch contacts, it also flows through the narrow strips 22 and 23 and thereby heats them. The metal of the element is so arranged that when it heats, the ends of the strips, that is, the ends at which they are joined to the tongue 24, bend downwardly and lift the free end of the tongue 24 adjacent the pin 2|, until it passes over the end of this pin. As soon as this happens the energized coil 6 draws the contacts to the lower position at which the thermostatic element is shunted or disconnected and immediately cools. If the current flow should be interrupted the coil becomes deenergized and the spring immediately pulls the contacts towards their upper position. The thermostatic element 1 having cooled immediately after the movement of the contacts to the lower position presses its tongue 24 against the pin 2| and the end thereof slips thereunder as soon as the contacts reach their upper position. With this arrangement, therefore, only a momentary interruption of current flow relatches the switch in its upper position. And even if such interruption occurs immediately after the movement of the switch to its lower position, this latching takes place since the movement of tongue 24 is not more than just past the end of the pin and the element cools so rapidly that even a moment after its operation it is cooled enough to prevent a reclosure of the switch.

The thermostatic element is also independent 91 ambient temperature; that is, the time element in the operation of the thermostatic element is the same under all temperatures within the normal range of outdoor temperatures. This is due to the action of the strips 22 and 23 and the tongue 24 of the element. Since each of these parts is subject to the same ambient temperature variations, they are equally flexed. The difierence in area of the members does not cause a change in the flexure of the members since the average temperature changes are sufiiciently slow to enable all parts to assume the same temperature. The flexing of the members 22 and 23 moves the tongue 24 since it is attached'to the ends of these members. The fiexure of the tongue 24 on the other hand, moves the free end of the tongue which is adjacent to pin 2|. Since the members are practically of the same length, the movement of the joined ends of 22 and 23 is substantially the same as the movement of the free end of 24. These movements are opposite to each other because of the manner in which they are supported. As stated above when the members 22 and 23 become heated, they flex downwardly and in doing so lift the opposite end of tongue 24. The tongue 24, however, also flexes due to ambient temperature and also bends its free end downwardly in response to a rise in ambient temperature. The movement of the tongue 24 imparted to it by the flexing of strips 22 and 23 is neutralized by the flexing of the end of 24 in the opposite direction and the result is that the end of the tongue always engages the pin 23 at the same point.

The operation of this device will be explained by reference to Fig. 2 which discloses the diagram of connection for a sodium electric discharge lamp controlled by the switch shown in Fig. 1.

Fig. 2 illustrates diagrammatically a sodium lamp 25, provided with two anodes 26 and 21 and two filamentary cathodes 28 and 29. cathodes are connected to autotransformers 3|] and 3|, which are in turn connected to 'the secondary winding 32 of a series transformer 33. The winding 32 is provided with a film cut-out device 34 and a radio frequency filter comprising a condenser 35 and a choke coil 36. When current flows in the main series circuit 31 and primary winding 38 of the transformer 33 is energized, current will flow from winding 32 through conductor-'39 to transformer 3|, from the transformer through conductor 40 to contacts I! and I8. At this time the spring |5 biases they switch arm 5, and the contacts I3 and I4 engage the contacts I! and I8. I Current, therefore, flows through the engaged contacts to the contact arms l0 and H, which are connected in multiple, conductor 4|, through the narrow strips 22 and 23 0f the element 1, conductor 42, autotransformer 30, conductor 43, coil 6, and through conductor to the other side of the winding 32.

The current flowing in the narrow strips 22 and is shunted by the movable switch member- It therefore cools immediately, The circuit during this latter position of the switch arm may be The . conductor 39, autotransformer 3|, conductors 45 and 46, to cathode 29, anode 21, across the discharge path to anode 26, cathode 28, conductors 41 and 48 to autotransformer 30, conductor 43, coil 6, conductor 44 to the other side of winding 32. In this position of the switch therefore the connection between the autotransformers is broken and current is forced across the discharge path in the lamp 25.

The lamp 25 .is of a type now known in the art and commonly referred to as a sodium lamp. It is provided with a pair of filamentary cathodes which are heated so as to vaporize the charge of sodium which is placed in this lamp. Although these lamps may be started at low temperatures and sufiiciently high voltage,"it is not advisable to start them in this manner because of the sputtering of the electrodes and the depositing of the opaque electrode material upon the enclosing glass container. This materially reduces the em- .ciency of the lamp.

The cathodes 28 and 29 are connected to their respective autotransformers 30 and 3| by the leads 45, 46, 41, and 48 in such manner that a higher current is obtained for heating the cathodes during the preheating period than during operation of the lamp. When switch 3 closes its circuit, the autotransformers are connected in series with each other so as to utilize the full primary windings thereof and thereby obtain the largest possible transformation ratio. The maximum current therefore flows through the secondary circuit and energizes the filaments to the preheating temperature. When the switch 5 opens the circuit between the transformers, a portion of the primary winding of each transformer is cut out so as to reduce the transformation ratio. Since the transformer 33 is connected to a constant, current circuit, the secondary current for energizing the filament is reduced and the cathodes are'heated to a lower temperature. Thus, referring to Fig. 2, when the circuit between conductors 40 and 42 is broken, the transformer windings between leads 46 and 4! become inactive. Consequently, the current in the windings remaining the same, the transformation ratio is reduced and a smaller current than before flows in the secondary circuit.

I claim:

1. In a thermally controlled switch the combination of a movable contact member and a stationary contact, means for normally biasing said member toward said stationary contact to close a circuit through said switch, a thermostatic element normally biased to latch said member in said circuit closing position,- means including a coil energized when current flows through said contacts tending to open said switch, means for heating said thermostatic element energized by current flowing through said switch contacts whereby said thermostatic element is moved to effect an unlatching of said switch member a predetermined time interval after each energization of said heating means, said heating means being deenergized at the instant "said switch opens whereby the thermostatic element cools and tends to return to latching condition immediately after the opening of said switch and relatches said movable contact member as soon as it returns to closed circuit position.

2. In a thermostatic switch, the combination of a movable switch member, means for normally biasing said switch member to a closed circuit position, a thermostatic element normally biased to latch said switch member in said closed circuit position, means arranged to bias said movable switch member to open circuit position energized simultaneously with the beginning oi current flow through said switch, means for heating said thermostatic element only during the closed circuit position of said switch member whereby said thermostatic element unlatches said switch member after a predetermined time period subsequent to the beginning of current flow through said switch and immediately cools so as to relatch said switch member in the closed circuit position when said member returns to this position responsive to its normal bias.

3. In a thermostatic switch, the combination of a movable switch member, a stationary contact, means for normally biasing said switch member so as to engage said stationary contact and thereby close a circuit through said switch, a thermostatic element connected in series with said movable switch member, a magnet coil energized at the instant at which current begins to flow through said switch arranged to bias said movable switch element to open the circuit through said thermostatic element, and means including said thermostatic element for latching said movable switch element in the closed circuit position until a predetermined interval of time subsequent to the instant of energization of said coil, said movable switch element being arranged to disconnect said thermostatic element and thereby cool it so that it will immediately move to relatch said switch in the closed position at the interruption of current flow through said coil.

4. In a switch, the combination of a movable contact member, a thermostatic latch comprising a rectangular bimetallic element having a pair of slots cut therein to form a pair of strips and a tongue supported at the joined ends of said strips, means forsupporting said strips at their free ends and for connecting them in circuit with said contact member, said tongue being normally biased into the path of said movable contact member to prevent its movement, and means responsive to current flowing through said switch and said thermostatic strips for moving said contact member, said tongue delaying the movement of said contact for a predetermined time after the beginning of said current flow.

5. In a switch, the combination of a movable contact member, a thermostatic latching element comprising a rectangular thermally responsive sheet having a pair of slots cut therein thereby forming a pair of strips and a tongue supported at the joined ends of said strips, means for supporting said element at the free ends of said strips, the free end of said tongue being normally biased to latch said switch member in closed circuit position, the bias of said free end being unafiected by ambient temperature variations due to the equal and opposite effect of the warping of said strips and said tongue in response to ambient temperature variations, and means for applying additional heat to said strips whereby the free end of said tongue is moved to unlatching position directly responsive to changes in the temperature of said strips caused by said additional heating means and independently of ambient temperature changes.

6. In a switch, the combination of a stationary contact and a movable contact member normally biased to engage said stationary contact to close a circuit through said switch, a thermostatic element comprising a rectangular bimetallic element having slots cut therein to form a pair of strips and a tongue supported at the joined end of said strips, means for supporting said thermostatic element at the free ends of said strips in circuit with said switch contacts, so that the free'end of said tongue normally moves under the end of said movable contact member when said contact member is in closed position, means for moving said movable contact member to open circuit position including a coil energized when current flows through said switch, said thermostatic element holding said switch closed for a predetermined period of time subsequent to the begin ning of current flow, said period being unaffected by ambient temperature variations.

WILLEM F. WESTENDORP. 

